The present invention relates to a multibeam radar sensor having a holder for a polyrod (pre-focusing element, also called a rod radiator).
Radar sensors in which polyrods are used for pre-focusing are known for example from PCT Publication No. 97/02496. Here a vehicular FMCW radar sensor for detecting objects is proposed, in which for example three transceive elements are attached to a lateral structure of a microwave strip conductor. In the beam path, a dielectric rod radiator (polyrod) is additionally attached before each antenna element, in order to achieve a better illumination of the dielectric lens and thus a pre-focusing. However, it has turned out that problem-free functioning of the rod radiator is ensured only if this radiator is positioned precisely. Even small deviations from the ideal position result in an overradiation of the lens, or a coupling with adjacent polyrods.
German Published Patent Application No. 197 10 811, describes a device for the directed radiation and/or reception of electromagnetic waves. This device is made up of at least one antenna element, a dielectric lens, and a dielectric element (polyrod) that is situated between the antenna element and the dielectric lens. This dielectric element is used to avoid overradiation of the dielectric lens and to pre-focus the electromagnetic waves radiated or received by the antenna element. For the simplification of the required exact adjustment, the dielectric element is extended in surface and is preferably fashioned in the shape of a pot. In this case as well, an insufficient decoupling of the electromagnetic waves is to be assumed, since the same dielectric element is used for all antenna elements.
A multibeam radar sensor is proposed in which a holder (of resilient construction) for polyrods, in connection with a spacing element, holds the polyrods fixedly at a predetermined spacing, preferably in the range between 0 mm and 0.2 mm. The stays of the holder are fashioned such that a spring force constantly presses the spacing element against the base plate. In this context, the spring force is chosen such that the maintenance of the predetermined spacing a is ensured even under disadvantageous operating conditions such as vibration, shock, and impact.